Triangle Seminars

Abstract:
AdS/CFT duality (or more general holographic principle) represents a major advance in understanding quantum gravity, and provides powerful tools for studying strongly coupled quantum field theories. This talk will give a basic introduction to AdS/CFT duality, with the focus on the computation of Witten diagrams and their Mellin transform. Witten diagrams, which play the role of Feynman diagrams, provide the means for computing correlation functions in AdS/CFT. We will show that CFT correlation functions obtained from Witten diagrams have much simpler structures after Mellin transform. Correlators in Mellin space are very analogous to the flat-space scattering amplitudes, and they are often called Mellin amplitudes. We will demonstrate the ideas by studying a few non-trivial examples.

Abstract:
This is the live session included as part of the LonTI lecture on Branes and the moduli space of instantons. Please register at https://lonti.weebly.com/registration.html to receive joining instructions for this live session which will be held via Zoom.

Instantons, or solutions to the self dual Yang Mills (SDYM) equations are well known solutions, introduced in the mid 70s and played a role in a host of applications in QFT and String Theory. This talk will show a simple brane construction which allows the computation of the moduli space of solutions to the SDYM equations, introduce the student to the world of quivers, and demonstrate simple computations which allow evaluations of these moduli spaces.
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Abstract:
In this talk I will sketch how we can test gravity with unprecedented precision by combining new gravitational wave measurements, observational bounds from cosmology, and novel particle theory inspired insights, in particular allowing us to zoom in on the nature of dark energy. In doing so, I will highlight the interplay between gravitational wave constraints on gravity post-GW170817, data constraints from cosmic microwave background and galaxy clustering measurements, and novel theoretical priors on such theories (ranging from purely classical stability requirements to radiative stability- and positivity-related priors).

[please email a.held@imperial.ac.uk for zoom link or password]

Abstract:
We briefly overview how historically string theory led theoretical physics first to algebraic/differential geometry, and then to computational geometry, and now to data science.

Using the Calabi-Yau landscape - accumulated by the collaboration of physicists, mathematicians and computer scientists over the last 4 decades - as a starting-point and concrete playground, we then launch to review our recent programme in machine-learning mathematical structures and address the tantalizing question of how AI helps doing mathematics, ranging from geometry, to representation theory, to combinatorics, to number theory.

Zoom Link: https://us02web.zoom.us/j/83496714171?pwd=bld3QmQ2c21laWxEWTd6ejVQbjZ5dz09 (contact dionysios.anninos@kcl.ac.uk for password)

Abstract:
Higher-Spin/CFT dualities are a promising playground to unravel the nuts and bolts of the AdS/CFT correspondence
away from supersymmetry, as the bulk and boundary descriptions are simultaneously perturbative. In this talk we demonstrate
how the free CFT three-point correlator involving two scalars and one conserved current of arbitrary spin organizes itself into the
dual AdS amplitude. Techniques from the embedding space formalism for AdS and CFT, as well as an insightful variation of Schwinger
parametrization, proposed in hep-th/0308184 play an important role. The talk will be based on arXiv:2009.10110.


Join Zoom Meeting
https://zoom.us/j/3515880979?pwd=MWU0V1ZOUzJ1eUozL1Vkb1RtbTZhZz09

Meeting ID: 351 588 0979
Passcode: the T word in AdS/CFT

Abstract:
In perturbative amplitudes in quantum field theory and string field theory, Cutkosky rule expresses the anti-hermitian part of a Feynman diagram in terms of sum over all its cut diagrams, and this in turn is used to prove unitarity of the theory. For D-instanton contribution to a string theory amplitude, the cutting rule needed for the proof of unitarity is somewhat different; we need to sum over only those cut diagrams for which all the world-sheet boundaries ending on some particular D instanton lie on the same side of the cut. By working with the closed string effective action, obtained after integrating out the open string modes, we prove that the D-instanton amplitudes actually satisfy these cutting rules, provided the effective action is real. The violation of unitarity in the closed string sector of two dimensional string theory can be traced to the failure of this reality condition. In the critical superstring theory, multi-instanton and multi anti-instanton amplitudes satisfy the reality condition. Contribution to the amplitudes from the instanton anti-instanton sector satisfies the reality condition if we make a specific choice of integration cycle over the configuration space of string fields, whereas contribution due to the non-BPS D-instantons will need to either vanish or have an overall real normalization in order for it to give real contribution.


(please email jung-wook.kim AT qmul.ac.uk for the zoom link)

Abstract:
I will discuss the integrability and wall-crossing properties of Kondo line defects in rational conformal field theories. It provides a large class of interesting defect RG flow starting from topological line defects. As a surprise, I will discuss new examples of the ODE/IM correspondence and our attempts towards its physical origin using 4d Chern Simons theory. This work is part of a multi-pronged exploration of studying 4D Chern-Simons theory as an overarching structure for integrable systems. –– Part of London Integrability Journal Club. New participants can register using the form at integrability-london.weebly.com. The link will be emailed.